1. Field of Invention
The present invention relates in general to improved trucks for railway cars. More specifically, but without restriction to the particular use which is shown and described, this invention relates to chevron shimming of the railcar's primary suspension.
2. Description of the Related Art
It is known that shimming a railcar's primary suspension compensates for railcar floor height loss when the railcar wheels become worn. It is also known that several methods for compensating for the loss of railcar height due to wheel wear can be utilized. For example, for rapid transit railcars which utilize chevron rubber springs, mounted directly into the truck frame, as the primary spring elements, shims may be applied under the side bearing load pad or at the central bearing if the truck has one. Another common method of shimming for wheel wear is to apply shims between the chevron spring and the truck frame. With this method, thin steel sheets bent to the same angle as the chevron springs are disposed between the chevron spring and the truck frame. However, with the aforementioned methods, the shims applied to compensate for wheel wear are separate items not readily available, are frequently lost in the retrofitting service shops, or are erroneously selected resulting in uncorrected railcar floor height.
Still another method for compensating for wheel wear includes trucks with the primary suspension having a chevron block between the chevron springs and the truck frame. While it is customary to shim at the side bearing load pad, it is also possible to place thin shims between the back of the chevron block and the truck frame. This brings the inside faces of the blocks closer together, which, due to the mating faces of the block and springs being on an angle, causes the block to seat on the springs sooner, thereby causing the truck frame to sit higher above the rail. Here again, the shims are separate items that can be lost or improperly selected.
Yet another method for wheel wear compensation includes adding shims between the top of the shelf extending out from the side of the wheel bearing housing and the bottom of the chevron spring. Again with this method, the shims are not readily available on the truck.
Still another method involves adding the shims between the bottom pedestal toe of the truck frame and the top surface of the lower portion of the chevron adapter. With this arrangement, it is necessary to remove the tie bar in order to apply the shims. As above, the shims are not readily available on the truck and are easily misplaced or improperly selected.
Shims on railway trucks are also used on the top of the bearing adapter and the bottom of the truck frame to maintain a given distance for the safety stop. This is done to keep from overextending the chevron spring and to insure that the working clearances in the truck will be maintained. Again, as with all the traditional methods of shimming for wheel wear, these shims are not carried with the truck, are frequently lost, or are simply not readily available.